1. Field of the Invention
This invention relates to a friction pad for use in a disc brake in which a lining member is secured to a surface of a backing plate.
2. Description of the Prior Art
A friction pad for a disc brake is disclosed in, for example, Japanese Utility Model Public Disclosure (KOKAI) No. 63-104738. The friction pad disclosed in this Utility Model publication includes a lining member secured to a surface of a backing plate by suitable means, such as an adhesive. A cavity is formed in the surface of the backing plate onto which the lining member is secured. The lining member is designed so that a portion of the lining member may be received in the cavity of the backing plate. The cavity may be formed by a press working of the backing plate. The opposite surface of the backing plate is provided with a protrusion at a position corresponding to the cavity, the protrusion being formed by the extruding of a portion of the material of the backing plate. According to this prior art friction pad, the cavity tapers in one direction, whereas the protrusion is columnar, i.e., the protrusion has a cylindrical outer periphery, so as to be received in a through-hole in a brake caliper of the disc brake. A torque applied to the lining member from a brake disc upon braking is transmitted to the backing plate by virtue of the resistance offered by the fixing means such as adhesive disposed between the backing plate and the lining member and a shearing resistance offered by the portion of the lining member which is received in the cavity. The torque is further transmitted from the backing plate through the protrusion to the caliper; thus the caliper finally receives the torque. In the friction pad disclosed in the above Utility Model publication, a respective cavity and protrusion are formed at three locations, two of the three protrusions being fitted within respective holes of the caliper, the remaining one serving to secure a retainer spring at a position which restricts free movement of the friction pad relative to the caliper.
It will be appreciated that a larger and deeper cavity is advantageous in terms of obtaining a high shearing resistance of the lining member. However, referring to FIG. 1 with respect to the above prior art friction pad, making the cavity A larger and deeper would cause the wall thickness t of the base portion of the protrusion B to be thinner, thus resulting in a backing plate which tends to be easily broken during pres working and a considerable reduction in the strength of the backing plate. The wall thickness of the base portion is especially reduced at the base portion of the protrusion which is fitted within the through-hole of the caliper since a relief groove is formed around the base portion of the protrusion for the purpose of ensuring that the protrusion will fit in the through-hole of the caliper. If it is intended to obtain a sufficient wall thickness t of the base portion of the protrusion, a height h of the protrusion B becomes smaller as shown in FIG. 2, thus disadvantageously reducing the effective area of the protrusion for transmitting torque to the caliper.